Underwater tracking ranges are used to track vehicles in operation. Traditionally this is accomplished using underwater acoustic triangulation systems. Acoustic pulses are transmitted from the moving underwater objects and received by a plurality (generally four or more) underwater hydrophones. By measuring the arrival time at these hydrophones in a synchronized time domain along with the positions of the hydrophones in x, y, z (latitude, longitude, depth) the vehicle position can be determined. These systems generally are good at tracking each vehicle at a different frequency or coded pulse so the range sets can be applied to a unique vehicle. These fixed systems are very expensive and complicated to use in portable applications.
Some general systems use underwater modems and transmit the vehicles position to a node that tracks the objects position. These modems send a large amount of data bits to transfer the position due to the very large overhead required by a modem. These modem system use a broadband signal and take up a large portion of the acoustic channel. They could interfere with underwater positioning system such as described in U.S. Pat. No. 8,009,516. If you transmit a range and bearing with 16s bit of precision using an acoustic modem with 100 bps data rate and 50% bit efficiency that will 16 bits/0.50=32 bits at 100 bps will use up over 32% of the data channel for a 1 second cycle. The current invention allows sending a range or bearing ping that is 0.5 ms in length will take up 0.05% of the data channel. This is important since many nodes can transmit the data in the same cycle for a shared cycle.
More flexible systems in operation use USBL (ultra short baseline) acoustic systems that can be mounted on a moving boat or moored. These devices use a related transponder/responder on the underwater vehicle that receives a signal and resolves a range and bearing. MicronNav-USBL Tracking System is one such system. These generally have limited range, high complexity and cost and limited resolution of bearing used to project the position.
The GIB-plus system, available from the ACSA subsidiary of the Alcen Group of Paris, France, is a system that uses four or more moored surface beacons that listen for pings from an underwater object. It can support up to 5 devices to be tracked, each requiring a separate frequency to resolve the ranges for triangulation. The beacons on the surface with radio links and GPS for position and timing log when the sound arrives from the device being tracked. The data from four beacons is transmitted by radio to a single computer that uses the time delays for each frequency pinger to triangulate a location with respect to each surface beacon. The device underwater that is being tracked doesn't know its own position.